Your only generally accepted as "true 5 volt devices" options AFAIK are:
Prodigy v1 - used
Prodigy v2 - sort of, it seems to be higher than the v1, but 5.x volts.
Great Lakes vapor GLV
Or various box style mods - I'm unaware of any that are sold commercially, but there may be.
Besides those, you could get a 5v USB passthrough, and ensure it has enough power to run properly, like a 2A or higher wall adapter, coupled to something like the Puresmoker USB Passthrough. Depending on the atomizer used, your PC likely doesn't provide full current to most passthroughs (USB2 IIRC, caps at 1A, although I think individual ports are only 500mAh).
The rest are 6-7v+ mods. The first 3 achieve 5.X volts by using a resistor inlines with either 3.0 or 3.6 volt
batteries. Note that a fully charged 3v Li-Ion battery measures ~3.6volts each, so you're starting off around 7.2v. A fully charged 3.7vDC battery starts around 4.2vDC, so up to 8+ volts from a pair.
Your other option is to buy a 'high voltage atomizer.' Some people swear by them, others, not so much. These can be had from GG suppliers, Nhaler, Eastmall and Ikenvape, possibly others. There are at least two versions of these, possibly more, 'meant for' 2x3v
batteries or 2x3.6v batteries. Even the '6v HV atties,' some claim they aren't much better than a standard e-cig battery and atomizer, others love them.
The 'HV atomizers' achieve their goal by building more resistance into the atomizer, instead of in the device itself. The reason for dissatisfaction, any quality issues aside, is IMHO, likely due to the amount of resistance for these atomizers. A 'normal' 510 atty will provide ~2.5Ohms of resistance. The '6volt 510 HV atomizer' I'm aware of provides nearly double that, at 4.5Ohms resistance. Let's see, on a normal 510 e-cig with a 3.7v battery, you are doubling the voltage almost exactly with a pair of fully charged 3v batteries (7.2v), and almost doubling the resistance as well - we can do the math for Ohms law, but at least it seems initially the 510 HV atomizers may not be the right resistance. I have a few, will think on and test later, and maybe realize I just posted something entirely off.
There are a few 'expected' mods coming in the not too distant future (hopefully?) that may add to the mix of true 5 volt loaded devices, or possibly one allowing adjustable voltages. Until then, those are your options AFAIK.